Hydrocode simulations of asteroid airbursts and constraints for Tunguska

A wide range of meteors were simulated impacting Earth's atmosphere using the ALE3D hydrocode. The size, density, strength curve, entry angle, and velocity of the meteors were varied to cover the parameter space of airbursts of interest to planetary defense in general which encompasses the Tunguska event in particular. The hydrocode simulations were used to calibrate a simple analytical model that can be used to quickly estimate the burst height of an incoming asteroid or comet. The hydrocode simulations show both rocky asteroids and icy comets are plausible Tunguska meteors, over a wide range of sizes, speeds, entry angles, at least in terms of the energy delivered and height of burst required to produce the tree-fall, and the lack of an obvious impact crater on the ground. This agrees with previous analytical estimates and hydrocode simulations of hypothetical Tunguska meteors, and provides a complete range of possibilities. Modelling of the tree wind resistance predicts windspeeds of 40–50 m/s are required to fell most of the trees. This is slower than previous estimates from nuclear test data, but faster than lower bound estimates from a 3 Mt blast. It suggests an energy of 10 Mt is most likely for Tunguska, but requires missing tree size distribution and wind response data to better narrow the probability distribution of potential Tunguska impactors.